1. Field of the Invention
This invention is directed to a method and apparatus for determining on-line core wide power output of a pressurized water reactor (PWR) using the excore detector system, and to correction of the same for changes in three-dimensional power distribution in the core and in coolant density.
2. Background of Information
The official determination of the reactor thermal power level in a PWR is based on a heat balance across the steam generators (S/G), called a secondary calorimetric measurement. The results of the calorimetric calculation are used to verify that the reactor is operating within the licensed reactor power level limits, and to calibrate the other indications of reactor power level.
This calorimetric calculation is performed off line. Other indications of reactor power level, such as excore detector signal levels and RCS loop temperature indication values, are periodically calibrated against the calorimetric and used to provide on-line reactor power level inputs to the reactor control and protection systems. Unfortunately, errors in the reactor thermal power level calculation cause errors in all the other indications of reactor power. Presently, there is no easy way to detect and correct small errors in the reactor thermal power calculation.
The major component of the heat balance calculation is the flowrate of feedwater into the S/G. The magnitude of the flowrate is typically determined using flow venturis installed in the main feedwater line for each S/G. The feedwater venturi flow readings are subject to systematic and random error mechanisms, which cause erroneous reactor power level calculation results. The most frequent systemic error, feedwater venturi fouling, causes the calculated reactor power to increase relative to the true reactor power level, necessitating a net reduction in the actual reactor power to maintain the apparent power within the operating limits. The amount of electrical output generated by the plant then decreases, reducing the revenue of the utility.
There is a need, therefore, for an improved method and apparatus for on-line measurement of reactor power which is not affected by random errors in the thermal power measurements.
There is also a need for a method and apparatus for correcting for errors in the calorimetric calculation of reactor power caused by feedwater venturi fouling or other types of systematic calorimetric error sources.